Amazon offers the Lipton Decaffeinated Black Tea 72-Count Box 2-Pack
(144 bags total) for $5.99. Add it to your cart via Subscribe & Save to cut it to $5.09 and bag free shipping. That's $0.04 per tea bag and $3 below the lowest total price we could find for this quantity elsewhere. (For further comparison, in March we saw 576 Lipton tea bags, although not decaf, for $16 with free shipping.)
Of note, be sure to cancel Subscribe & Save after your order arrives to avoid being billed for subsequent shipments.
Update: The price has since risen to $7.06 before discounts. However, clip the $2 off coupon and add it to your cart via Subscribe & Save to lower it to $4 with free shipping.